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Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2054 - 2057, 2015/10
Times Cited Count：1 Percentile：8.67(Nuclear Science & Technology)Reduced activation ferritic/martensitic steel, as typified by F82H, is a promising candidate for structural material of DEMO fusion reactors. To prevent plasma sputtering, tungsten (W) coating was essentially required. This study aims to examine the irradiation effects on hardness and microstructure of vacuum-plasma-spray coated W-F82H steel, with a special emphasis on the impacts of grain-refining induced by frictional stir processing (FSP). It was revealed that the hardness of the VPS-FSP W after ion-irradiation to 5.4 dpa at 800
C were not remarkably changed, where bulk W usually exhibited significant irradiation hardening.
Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10
Times Cited Count：14 Percentile：71.37(Nuclear Science & Technology)The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.
Nozawa, Takashi; Ozawa, Kazumi; Asakura, Yuki*; Koyama, Akira*; Tanigawa, Hiroyasu
Journal of Nuclear Materials, 455(1-3), p.549 - 553, 2014/12
Times Cited Count：17 Percentile：74.92(Materials Science, Multidisciplinary)SiC/SiC composite is a promising candidate material of fusion DEMO reactor. This paper aims to identify its damage tolerance and strength anisotropy by various characterization techniques such as acoustic emission (AE) monitoring, electrical resistivity (ER) measurement, and digital image correlation (DIC). The AE results identified that damage accumulation initiated prior to the proportional limit stress (PLS) by both tensile and compressive loadings for 2D composites. The preliminary AE waveform analysis implied that this AE detect strength corresponds to initiation of micro-cracking but the stress-strain curve shows further linearity due to the strong interfacial friction. Then fiber sliding occurred near the PLS, followed by the non-linearlity of the curve. The preliminary tensile test results using a notched specimen also suggest notch insensitivity of the composites in any loading directions. The detailed failure mechanism will eventually be discussed with ER and DIC results.
Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10
Times Cited Count：13 Percentile：66.18(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 88(9-10), p.2543 - 2546, 2013/10
Times Cited Count：16 Percentile：73.38(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate for a fusion DEMO blanket. Due to the inherent quasi-ductile failure of composites, determining failure scenario for this class of composites is undoubtedly important to develop design codes in practical use of them. This study aims to evaluate the failure behavior of the quasi-ductile SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique. The AE results distinguished damage accumulation processes by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the PLS by both tensile and compressive loadings because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface. In this paper, an updated failure envelope will be provided by referring the actual matrix cracking stresses as more realistic and reasonable failure criteria.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11
This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.
Nozawa, Takashi; Ozawa, Kazumi; Choi, Y.-B.*; Koyama, Akira*; Tanigawa, Hiroyasu
Fusion Engineering and Design, 87(5-6), p.803 - 807, 2012/08
Times Cited Count：35 Percentile：89.95(Nuclear Science & Technology)A SiC/SiC composite is a candidate material for a demonstration fusion power reactor. Considering the inherent anisotropy of composites with variety of fabric architecture is required to precisely predict axial and off-axial mechanical properties by various failure modes. This study evaluated crack propagation behavior by the various modes to provide a strength anisotropy map and we discussed a methodology to analytically predict this trend. The strength anisotropy maps identified for various fabric orientations clearly indicate that the composites failed by the mixed modes. Specifically, due to the axial anisotropy, five individual modes such as tensile/compressive strengths in the axial/transverse directions, respectively, as well as the in-plane shear strength, are identified to be essential. In this study, with the analytical criterion based on the Tsai-Wu model, the strength anisotropy could satisfactorily be described.
Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.
JAEA-Technology 2009-072, 144 Pages, 2010/03
JAEA-Technology-2009-072.pdf:45.01MB
"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.
Nozawa, Takashi; Nakata, Toshiya; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Toyoshima, Kazuoki*; Tanigawa, Hiroyasu; Hinoki, Tatsuya*
no journal, ,
An advanced SiC/SiC composite is a promising candidate material for fusion DEMO blanket. Current study preliminarily aims to examine tensile deformation behavior of unirradiated advanced SiC/SiC composites tested at high temperatures. In rupture tests being concurrently conducted at 1000C in vaccum, it was revealed that the plain-woven CVI-SiC matrix composite reinforced with Tyranno-SA3 fibers did not fail at 174 MPa (equivalent to 130% of PLS at 1000C) for 1986 hours. Presently there was no negative sign of the notch effects, implying their good rupture property at certain conditions of concern.
Ozawa, Kazumi; Kondo, Sosuke*; Nozawa, Takashi; Tanigawa, Hiroyasu; Hinoki, Tatsuya*
no journal, ,
A SiC/SiC composite is a promising material for fusion DEMO reactor. In this presentation, dimensional and microstructural stabilities of advanced SiC fibers after high-dose ion irradiation at the temperature, where the composite is to be used as a flow channel insert (FCI), were evaluated by step height measurement and FE-TEM, respectively. As a preliminary result using the step height measurement, matrix and fiber was relatively flat and had no significant gap in a Tyranno-SA3 composite after ion irradiation at 600C to 100 dpa, while in a Hi-Nicalon Type-S composite a hollow part was observed in the center of the fiber. Differences of two types of advance SiC fibers on microstructure were discussed, compared with previous neutron/ion- irradiated data, considering the issues associated with ion irradiation and effects of pyloritic carbon interphase.
Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
no journal, ,
no abstracts in English
Nozawa, Takashi; Park, J.-S.*; Nakazato, Naofumi*; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
Silicon carbide is a candidate nuclear materials because of low-activation and superior irradiation resistance as well as perceived various characteristics inherently featured as prominent engineering ceramics and a continuous fiber reinforced composite has generally been developed due to brittleness of SiC itself. Of many material parameters for design, validation of high temperature durability at approximately 1000C is essential. Understanding of anisotropy of woven composite strength is also very important. Besides, developing comprehensive model to predict composite strength by various modes with a limited data set. This study aims to summarize the features of fracture behavior by tensile, compressive and shear at elevated temperatures. With consideration of the prediction model, we finally obtain the high temperature strength anisotropy map.
Usami, Koji; Ichise, Kenichi; Numata, Masami; Endo, Shinya; Onozawa, Atsushi; Takahashi, Hiroyuki; Kikuchi, Taiji; Ishikawa, Kazuyoshi; Yoshikawa, Katsunori; Nakata, Masahito; et al.
no journal, ,
In the R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant, the specimens to be obtained by coupling irradiation between JOYO and JRR-3 is necessary to establish the evaluation method by using the irradiation damage indicator of them. Therefore, the techniques for assembling of JRR-3 re-irradiation capsule in the Waste Safety Testing Facility (WASTEF) were developed to perform the coupling irradiation. The techniques contributed to the first coupling irradiation in the world.
Hamaguchi, Dai; Morisada, Yoshiaki*; Fujii, Hidetoshi*; Tanigawa, Hiroyasu; Ozawa, Kazumi
no journal, ,
Friction-Stir Process (FSP) were applied to OFCCu and ITER-Gr CuCrZr cooling pipe in order to evaluate the applicability of the process to mechanically strengthening pure-Cu and possible structural improvement on CuCrZr alloy. Former study revealed that the achievement of very fine grain structure at certain rotational speed and also the hardness increase to about 1.5 time higher within the stir-zone but also relatively shallow stir-zone depth compared to a length of the pin and rapid void formations. In order to avoid this phenomenon, compulsory cooling with liquid Co
during the process was introduced, and the results showed the absence of void formation at relatively lower rational speed of around 300 RPM and also maintaining the effective stir-zone to relatively higher rotational speed compared to non-cooling tests. Similar FSP tests with compulsory cooling were also applied to ITER-Gr CuCrZr cooling pipe for divertor application. The detail will be reported on the presentation.
Ozawa, Kazumi; Kato, Yutai*; Nozawa, Takashi; Snead, L. L.*
no journal, ,
Advanced SiC/SiC composites are candidates for the advanced blanket material for fusion DEMO reactor. In order to investigate the effects of neutron irradiation on fracture resistance, the composites after neutron irradiation to 
5.9 
10
n/m
(
0.1 MeV) at 800 and 1300C were evaluated by three-point single edge notched bend miniature test. Taking all results into consideration for the global energy balance analysis based on the non-linear fracture mechanics, the previous tensile tests, and the hysteresis loop analysis for interfacial property evaluation, it was concluded that the effects of neutron irradiation in conditions studied on fracture resistance of the composites appeared insignificant.
Ozawa, Kazumi; Kato, Yutai*; Nozawa, Takashi; Tanigawa, Hiroyasu; Snead, L. L.*
no journal, ,
An advanced SiC/SiC composite is very attractive as an advanced blanket material for fusion DEMO reactor. In this study, tensile and fiber/matrix interfacial properties of unirradiated SiC/SiC minicomposites were evaluated in order to examine the effects of difference of fiber and interphase thickness. The experiments revealed that fiber surface roughness directly correlates with interfacial sliding stress and that the relationship can affects ultimate tensile stress. Additionally the dependence of interphase thickness on tensile and interfacial strength was also confirmed.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
Tensile and interfacial properties of unidirectional SiC/SiC model composites reinforced with Hi-Nicalon Type-S fibers with innermost pyrolytic carbon (PyC) layer thickness of 240 and 1150 nm (TypeS-240 and TypeS-1150, respectively) were evaluated by unloading/reloading cyclic tensile tests and single fiber push-out tests. Effective fiber bundle strength in the TypeS-240 and -1150 composites were 79-104% and 70-85%, compared with the original fiber bundle strength. According to the analytic results using hysteresis loops of tensile curves, interfacial sliding stress of the TypeS-1150 estimated to be about 0.7 times as large as the TypeS-240. This tendency was also confirmed by the single fiber push-out tests. These composites showed quasi-ductility, but it is considered that the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. In order to design a damage tolerant composite, fiber/matrix interfacial properties with and without irradiation effects should be thoroughly and systematically understood. For this purpose an approach using model composites is considered to be suitable. This study examines the effects of different fibers and interphases on tensile and interfacial properties of non-irradiated SiC/SiC minicomposites which have high crystalline and near stoichiometric SiC fibers. As a result of the tensile unloading-reloading cyclic tests, following analysis of the hysteresis loops, and the single fiber push-out tests, (1) fiber surface roughness can significantly affect interfacial sliding stress and hence each tensile characteristic such as tensile strength/strain and hysteresis loop width, and (2) interphase thickness would also influence the interfacial and tensile properties.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu; Kato, Yutai*; Snead, L. L.*
no journal, ,
A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. Unloading-reloading cyclic tensile tests were conducted to estimate interfacial properties for unidirectional SiC/SiC minicomposites reinforced by Hi-Nicalon Type-S (HNLS) or Tyranno-SA3 SiC fibers via CVI process were conducted. The interfacial properties were also evaluated by fiber push-out test. According to these results, it is implied that both fiber surface roughness and interfacial layter thickness can impact the tensile and interfacial properties.
